3 pi nu_tau > Isospin violating signals in the tau → 3 pi nu_tau decay mode are
discussed. For the tau → pi^- pi^- pi^+ nu_tau decay mode, isospin
violation arises from the vector current contribution in the
tau → omega pi nu_tau decay with the subsequent isospin violating omega
decay into pi^+ pi^-. We demonstrate that such effects may be observed in
presently available data through the measurement of the interference
effects of these vector current contributions with the dominating axial
vector current, i.e. through a measurement of the structure functions
W_F,W_G,W_H and W_I. In the case of the tau → pi^0 pi^0 pi^- nu_tau decay
mode, a vector current contribution is generated by eta pi mixing in the
decay chain tau → eta rho nu_tau → pi^0 pi^0 pi^- nu_tau. We find that
this effect is rather small, the magnitude of the associated interference
terms being too low for present statistics.